With winter approaching I have began doing oil changes for the winter. The new cars go to the dealer but I have an old Silverado with the 4.8 that I bought new in the fall of 99. Always done once every 6 months of AC Delco full synthetic in it. The past 5 years it hasn’t gotten ran much maybe 500 miles a year but I still have stuck to the 6 month oil change interval regardless of miles. The last time it only had a few hundred miles but I changed it anyway since it had been 6 months. Truck is in great condition no rust or anything on the body and always garage kept so I’d like to keep her around as long as I can. My question is am I wasting money doing it once every six months regardless of the mileage or should I bump it to once a year?